(a) Field of the Invention
The present invention relates to a tip mechanism for a knock-type ballpoint pen and, more particularly, to a tip mechanism for a knock-type ballpoint pen which can perform a ball pressurizing function in an appropriate manner.
(b) Description of the Related Art
Generally, ballpoint pens make use of water gel ink or oil gel ink which has a high viscosity at a static state but has a reduced viscosity at writing with the application of shearing force through rotation of the ball. Such ballpoint pens are classified into a tip covering type of exposing a tip portion to the outside with a separate tip cover at all times and a knock type of exposing the tip portion to the outside only at writing without the separate tip cover.
The usual knock-type ballpoint pen includes a barrel-shaped case with a one-sided conical portion and an opposite sided knocking member, an ink storing tube disposed within the barrel-shaped case, and a tip mechanism with a ball positioning end and an opposite end inserted into the ink stroring tube. The tip mechanism is provided with a small metal ball and an elastic member for pressurizing the ball.
In this structure, when the pen is put on a paper, the ball is pressed and an opening path is made around the ball. At this time, ink fed to the tip mechanism from the ink storing tube flows over the ball through the opening path and is transferred onto the paper. When the pen is withdrawn from the paper, the elastic member pressurizes the ball and the opening path is closed to intercept flowing of ink.
In such a tip mechanism, a coil spring is used for the elastic member with a linearly extended ball-pressing portion which is adapted to the narrow space of an ink guide hole. The linearly extended ball-pressing portion conventionally has a diameter of 0.1.about.0.3 mm. Therefore, the ball-pressing portion is formed with a sharply pointed shape which is liable to intervene rotation of the ball and scratch or crack an external surface of the ball. This prevents the ball from smoothly rolling with a fluent ink flowing and causes ink spot at writing or disconnected portions at line drawing.